Stories similar to sadc hangs causing machine to partly seize up.

I was half way through an upgrade from 12.04 to 14.04 when my machine crashed. At this point it had been running for over an hour doing the upgrade so I have no idea what caused it. I was merrily reading a book when the machine just rebooted. I am pretty convinced it was only about one third done with the upgrade.

Unfortunately it did not even get to the login screen after the reboot.